在 Quitting an application - is that frowned upon? 中，很多人探讨了android中退出app的问题，
Google官方是这样说的：
Question: Does the user have a choice to kill the application unless we put a menu option in to kill it? If no such option exists, how does the user terminate the application?
Answert (Romain Guy): The user doesn't, the system handles this automatically. That's what the activity lifecycle (especially onPause/onStop/onDestroy) is for. No matter what you do, do not put a "quit" or "exit" application button. It is useless with Android's application model. This is also contrary to how core applications work.
不过，新浪微博，微信，米聊，按菜单，都有退出选项。
所以，我觉得菜单中有退出也还好。
